Starters for starting engines incorporate therein an electromagnetic switch operative to shift a pinion to a ring gear and to open or close a main contact provided in a motor circuit; the motor circuit is a circuit for allowing current from a battery to a motor.
When the motor is energized, that is, the electromagnetic switch closes the main contact, a high current flows from the battery through the motor as in-rush current. The occurrence of the in-rush current may cause the terminal voltage of the battery to significantly drop, so that a phenomenon, referred to as “short break”, in which electric devices, such as meters and audio devices, instantaneously stop working, may occur.
In order to address such a situation, the present applicant has proposed a technology to reduce in-rush current flowing when the motor is energized to prevent the occurrence of “short break” (see a first patent document).
Referring to FIG. 12, an invention disclosed in the first patent document is comprised of, in addition to an electromagnetic switch 101 incorporated in a starter 100, a motor energizing relay (an electromagnetic relay) 102 operative to open or close a motor circuit. Referring to FIG. 13, the relay 102 is comprised of a resistor 105 connected with the motor circuit via two terminal bolts 103 and 104, and a relay contact 106 between an upstream end and a downstream end of the resistor 105; the relay contact 106 consists of a pair of stationary contacts. The relay 102 is operative to open or close the relay contact 106 by a movable contact 108 that can be moved depending on the energized state of a relay coil 107. The energized state of the relay coil 107 is controlled by a drive signal outputted from a control circuit 109 (see FIG. 12). For example, the relay coil 107 is energized to close (turn on) the relay contact 106 when the drive signal of the control circuit 109 is on, and de-energized to open (turn off) the relay contact 106 when the drive signal of the control circuit 109 is off.
When the motor 110 is activated, the drive signal of the control circuit 109 is off, so that the relay contact 106 is opened with the relay coil 107 deenergized. As illustrated in FIG. 12, a current limited by the resistor 105 flows through the motor 110 when the electromagnetic switch 101 closes the main contact 111 in this state. This causes the motor 110 to be turned at a low speed. Thereafter, that is, after engagement of a pinion 112 of the starter 100 with an engine-side ring gear 113, the drive signal is switched from off to on. This results in excitation of the relay coil 107, which closes the relay contact 106. The closed relay contact 106 causes both ends of the resistor 105 to be short-circuited via the relay contact 106. The short-circuit of both ends of the resistor 105 allows the full voltage of a battery 114 to be applied to the motor 110, so that a current higher than that at activation of the motor 110 flows through the motor 110. This increases the rotational speed of the motor 110.